The invention relates to a brake-force split gear for a parking-brake system operated by muscular power and belonging to a motor vehicle, in which the brake force is transmitted via cable assemblies both to a wheel brake or shaft brake on the vehicle transmission and to wheel brakes of at least one driven vehicle axle, the wheel brakes of each vehicle axle being articulated in each case via a differential element mounted in a housing or frame, and the split gear being a lever mechanism comprising at least one balance beam which splits the brake force between the transmission brake and wheel brakes.
A brake-force split gear of this type is known from DE 197 33 552.7 which is not a prior publication. A lever mechanism is described there, which is arranged on a housing and comprises both an operating lever and a balance beam. The operating lever and the balance beam are coupled to one another via a pivoting joint. A differential element together with the wheel-brake cable assembly is mounted in an articulated manner at one end of the balance beam, whilst the transmission-brake cable assembly is suspended at the other end. The entire mechanism is arranged in and on a housing in front of the rear vehicle axle and between the vehicle frame. By virtue of the lever arrangement, the operating cable assembly articulates the housing eccentrically, as seen in the top view. Consequently, a cable assembly led in a protective tube is necessary for operating the parking-brake system, so that the split gear can be used both in a vehicle with left-hand rive and in a vehicle with right-hand drive.
The problem on which the invention is based is, therefore, to provide a brake-force split gear which ensures a sufficient engaging action on a road with unequal grip, even in the event of a failure of part of the brake system. The split gear is to be designed as a module, along with a low construction-space requirement, a low outlay in terms of maintenance and simple adjustability, and is to require the same components both for a vehicle with right-hand drive and for a vehicle with left-hand drive.
The problem is solved by means of the features of the main claim. The differential element arranged in the housing or frame is mounted on a lever in the region between the ends of the latter. The lever is pivotably fixed at one end to the housing or frame and is suspended at the other end in a lever-mechanism cable. The lever-mechanism cable and the cable assembly leading to the transmission brake are articulated on the balance beam which, if appropriate, is positioned at a distance, an articulation point for the operating cable or an operating element being located in the region between the articulation points for the lever-mechanism cable and the transmission-brake cable assembly.
The brake-force split gear splits the brake operating force via the balance beam and the cable assemblies in such a way that the braking action of the wheel brakes sufficiently conforms to the legal and/or factory standard for the braking action on a road with unequal grip. In this case, a large proportion of the brake operating force is allocated to the highly effective transmission brake. If, for example, dual power brakes are used for the transmission brake and the parking brakes of the wheels, then, for example, each wheel brake of an axle receives 35% and the transmission brake 30% of the operating force. The combination of transmission and wheel brakes also makes it possible still to have a high braking action on a road with unequal grip even in the event of a failure of one wheel brake. If, for example, the wheel having the failed parking brake stands on a smooth icy surface, the wheel standing on a road section with good grip prevents the vehicle from slipping away in spite of a considerable loss of brake force. This is because the transmission brake, jointly with the parking brake with is still working, locks the axle differential, so that the engaging of the wheel standing on the icy surface takes place via the differential due to the locking of the wheel standing on the road section with good grip. The wheel standing on the icy surface cannot rotate and therefore cannot even begin to roll at all.
These and other objects and advantages are achieved by the brake force splitting gear according to the invention, in which the differential element arranged in the housing or frame is mounted on a lever in the region between the ends of the latter. The lever is pivotably fixed at one end to the housing or frame and is suspended at the other end in a lever-mechanism cable. The lever-mechanism cable and the cable assembly leading to the transmission brake are articulated on the balance beam which, if appropriate, is positioned at a distance, and an articulation point for the operating cable or an operating element is located in the region between the articulation points for the lever-mechanism cable and the transmission-brake cable assembly.